1. Field of the Invention
The present invention relates to a packet multiplexing system which divides input data into a plurality of packets to multiplex the packets for output. The invention relates particularly to a packet multiplexing system which compares input data with the corresponding data in a packet.
2. Description of the Prior Art
MPEG2 (Moving Picture Expert Group 2), one of encoding systems for compressing moving pictures, has been used to generate packets of various types of data such as image data, voice data, text data, and so forth. These packets are multiplexed, recorded on recording media, and sent over communication lines. MPEG2 defines the recommendations for a unit receiving multiplexed packets, that is a de-multiplexing system, but not for a multiplexing system. Therefore, a multiplexing system may be designed as long as a de-multiplexing system satisfies the recommended performance.
A conventional packet multiplexing system has the video PES packetizing module 61, voice PES packetizing module 62, private data PES packetizing module 63, and TS/PS packetizing module 64 as shown in FIG. 2. The three packetizing modules, video PES packetizing module 61, voice PES packetizing module 62, and private data PES packetizing module 63, packetize elementary streams (ES), such as video data, voice data, and private data, respectively, which are sent from the encoding module (not shown). The packetizing modules 61, 62, and 63 then generate packetized elementary streams (PES) shown in FIG. 3. Next, the TS/PS packetizing module 64, in turn, packetizes those PESs, generate transport streams (TS) or program streams (PS) shown in FIGS. 4 and 5, and outputs them.
In addition, this packet multiplexing system compares non-multiplexed data and multiplexed data in the stream to check if input data is set up correctly in the stream. More specifically, the packet multiplexing system has a circuit (not shown) functionally equivalent to the packet de-multiplexing module which should be in a de-multiplexing system. This circuit, almost as large as the multiplexing system in size, de-multiplexes the multiplexed transport streams (TS) or program streams (PS) into elementary streams (ES); that is, video data, voice data, and private data elementary streams (ES), and then checks if the de-multiplexed elementary streams (ES) match the original elementary streams (ES).
However, the monitor circuit in the conventional packet multiplexing system is too large and expensive, which leads to difficulties to provide a compact and low-cost packet multiplexing system.